System for controlling separating gravity in dense-media cyclone

ABSTRACT

This invention is directed to a method of beneficiating a material, such as coal, by subjecting the coal to be treated to the action of a dense-media cyclone, where the dense-media thereof is a slurry of magnetite in water. More particularly, the present invention relates to a method to control the separating gravity of said cyclone within predetermined limits by (1) measuring the flow rate and percent magnetite in the flow discharging from the cyclone, and (2) based on pre-calibrated data, adjusting the feed flow and content, i.e. magnetite and/or water, into said cyclone, thereby controlling said separating gravity within predetermined limits.

BACKGROUND OF THE INVENTION

The present invention is directed to a method of beneficiating material,such as coal, by the sink-and-float process utilizing a dense-mediacyclone. More particularly this invention relates to such method inwhich the separating gravity of the dense-media cyclone is controlled toinsure the optimum beneficiation of the treated material.

The use of dense-media separators for segregating material according toits specific gravity is well known in the material separating art, suchas the processing of coal. In these separators, a dense-media formed ofa finely divided high gravity solid, such as magnetite, suspended inwater, is maintained within a vessel, i.e. cyclone. The material or coalto be separated is introduced into the dense-media, and the material orcoal which has a specific gravity less than the specific gravity of thesuspension reports to the cyclone overflow. For convenience, the coalmay be termed the overflow. Material or refuse which has a specificgravity greater than the suspension reports to the cyclone underflow.Thus, the sink material may be termed the underflow.

By the very nature of this beneficiating process, the coal and refuse,overflow and underflow respectively, entrain a certain quantity of themagnetite which must be removed from the coal if the coal is to bethoroughly cleaned for commercial use. Further, recovery of themagnetite, which may be re-used in the process, is necessary for anefficient and economical process. While the present invention relatessolely to the primary separation of the coal from the refuse, themagnetite recovery step suggests a further feature of the process, andthat is the need to replenish the dense-media suspension. Inreplenishing the suspension care must be taken to insure a suitablespecific gravity within predetermined limits in the cyclone to achievethe primary separation.

A conventional method of controlling the specific gravity of theseparating vessel has been for the operator to check the specificgravity of samples of the dense-media at regular intervals and manuallymake adjustments based on such checks. Another method involves measuringthe specific gravity of the media continuously as it enters the vesseland adding water or magnetitie when necessary. Such methods, even whenautomated, had disadvantages.

U.S. Pat. Nos. 3,246,750 and 3,247,961 (Chase et al), each entitled,"Method and Apparatus for Controlling Specific Gravity in a Heavy MediumProcess," teach a system for separating mineral particles, such as coal,which system in part includes "measuring a specific gravityrepresentative of the suspension in the vessel." Based on thismeasuring, adjustments are made to bring the vessel's specific gravitywithin predetermined limits.

Controls for the systems described in the above patents rely upon theneed to maintain a constancy within the cyclone to obtain an optimumclassification of products therefrom.

The present invention represents a unique approach to obtaining aprecise separating gravity in a dense-media cyclone usingmagnetite-water as the slurry therein. Specifically, this inventionresulted from the recognition in the processing of coal that there is acorrelation between the quantity of magnetite in the cyclone overflowand the separating gravity of the cyclone. The manner by which suchrecognition has been incorporated into the system of this invention willbe described in the following specifications.

SUMMARY OF THE INVENTION

This invention relates to a method of beneficiating a material, such ascoal, by subjecting the coal to be treated to the action of adense-media cyclone, where the dense-media thereof is a slurry ofmagnetite in water. Since, as discovered herein, the separating gravityin a dense-media cyclone is a function of the distribution of themagnetite between the overflow and underflow discharging from thecyclone, the present method controls the separating gravity of thecyclone within predetermined limits by (1) measuring the flow rate andpercent magnetite in the overflow, for example, discharging from thecyclone, and (2) based on pre-calibrated data, adjusting the feed flowand content of additional magnetite and/or water, into the cyclone,thereby reestablishing said separating gravity to within predeterminedlimits.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a dense-media cyclone circuitincorporating means for controlling the separating gravity in saidcyclone according to this invention.

FIG. 2 is a graph illustrating the relationship between the separatinggravity of a dense-media cyclone, and the percent magnetite in theoverflow from said cyclone.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

This invention is directed to a method of beneficiating material, suchas coal, by the gravimetric process. It should be understood that suchprocess is merely one of several steps in the beneficiation of material.That is, the overall process may include (1) particle sizing, (2)cyclone separation, and (3) washing and screening, prior to obtainingusable material. While each step involves specific technologies, thepresent invention is directed only to the intermediate step noted above.

Turning now to such intermediate step with particular reference to FIG.1, typically raw coal (feed) is directed into a dense-media separator orcyclone 10 which utilizes the specific gravity of the media to separaterefuse from the coal. In the case of coal, a slurry of coal, magnetiteand water, is fed into cyclone 10. Make-up magnetite valve 12 andmake-up water valve 14 are continuousy adjusted, in a manner to bedescribed hereinafter to provide a feed density greater than 1.00. Suchfeed density is monitored by meter 26 while the flow rate and percentmagnetite of the feed are monitored by meters 22 and 24, respectively.

In operation, controlled amounts of magnetite and water are added to thecyclone 10 to achieve a separating gravity within prescribed limits,typically 1.30 to 2.00. Separating gravity as used herein means thespecific gravity at which a particle has an equal chance of reporting tooverflow or underflow, or where 50% of the particles that have aspecific gravity equal to the separating gravity report to the overflowand 50% to the underflow.

The present invention is based on the discovery that the separatinggravity in a dense-medium cyclone, in which water and magnetite aremixed to form the slurry feed to the cyclone, is a function of thedistribution of the magnetite between the overflow and underflow. Thatis, by measuring the flow rate and percent magnetite in one or each ofthese streams, the percent reporting to either the overflow or underflowcan be determined. FIG. 2, for example, is a graph showing therelationship of the separating gravity in the cyclone versus the percentmagnetite in the overflow. Thus, by monitoring the respective streamsfrom the cyclone changes in the percent magnetite may be readilyobserved and appropriate changes made to the feed of water and magnetiteto the cyclone.

The monitoring of the change in magnetite and the appropriate changes tothe feed make-up can be accomplished automatically. Referring again toFIG. 1, after the overflow, i.e. clean coal, and the underflow, i.e.refuse, leave the cyclone 10 a flow meter 16 and a coil 18 measure theflow rate of slurry in GPM and percent magnetite in each respectivestream. These measurements are transmitted to a micro-processor 20 whichcalculates the percent magnetite and compares it to a pre-calibratedcurve to determine the separating gravity. If corrections are requiredthe microprocessor 20 transmits a signal to the appropriate valve 12,14to add magnetite or water, whichever is required to change theseparating gravity. Simultaneously, a flow meter 22 and coil 24 on thefeed measure the GPM of slurry and percent magnetite. These measurementsare transmitted to the micro-processor 20 for comparison with thepreviously calculated values. Finally, a density gauge 26 may beincorporated into the system to monitor the feed density and to controlthe amount of non-magnetic material, i.e. water, being circulated.

As reported earlier in describing the general operation of a dense mediacyclone, recovery of the magnetite from the overflow and underflow isvital to an economic operation. By recovering the magnetite it ispossible to reuse same in the system. Accordingly, recirculating means28 are provided for supplying or delivering the recovered magnetite forreuse in the system of this invention. Thus, the input or material feedto the cyclone is derived from several sources. The non-magnetites, i.e.raw coal to be cleaned has been designated "Feed" in FIG. 1.Recirculated magnetite, and water, since the magnetite is not in a drystate, are fed to the cyclone by means 28. Finally, since magnetiterecovery from the cleaned coal and refuse is not 100%, make-up magnetiteand water are introduced into the cyclone by valves 12 and 14.

The method of this invention may be illustrated best by way of aspecific example.

EXAMPLE Equipment

a. Cyclone 10-ten (10) inch diameter; the capacity is estimated to befifteen (15) TPH feed solids operating at an inlet or feed pressure of20 psi.

b. Micro-processor 20-Hewlett-Packard model HP85, manufactured byHewlett-Packard Co.

c. Flow meters 16,22-magnetic flowmeter model 10D1416F, manufactured byFischer and Porter Co.

d. Coil 18,24-Ramsey Coil model 30-21, manufactured by RamseyEngineering Co.

e. Density gauge 26-Texas Nuclear model SGH, manufactured by TexasNuclear Co.

Operation

The input or material feed to the cycone 10 can be expressed TPH (tonsper hour) or GPM (gallons per minute). For such 10" diameter cyclone,the material feed from the several sources comprises:

water--46 TPH, (185 GPM)

non-magnetics--15 TPH, (45 GPM)

magnetite--25 TPH, (20 GPM)

Based on such breakdown of the material feed, a typical separatinggravity for the cyclone is 1.40. However, during processing of the coalsuch separating gravity may change affecting the separation of the coalfrom the refuse. By the method of this invention, the separating gravitymay be readily restored to the desired level.

For the 10" diameter cyclone of this Example, and from the operationdata presented above, the feed input is 250 GPM. Consequently, theoutput between the overflow (clean coal) and underflow (refuse) totals250 GPM. If the feed input includes 25 TPH of magnetite, then 25 TPH ofmagnetite will exit the cyclone in the overflow and underflow streams.The present invention is based on the recognition of a correlationbetween the magnetite in the overflow (or underflow) and the separatinggravity of the cyclone. If the coil 18 shows, for example, that 20% or 5TPH of magnetite is present in the overflow stream, a review of FIG. 2will show that at 20% magnetite reporting to cyclone overflow theseparating gravity of the cyclone will have increased slightly to about1.41. The percent magnetite passing through coil 18 is continuouslymonitored and the appropriate data transmitted to microprocessor 20. Ifthe separating gravity of the cyclone increases or decreases to anunacceptable level, microprocessor 20 will transmit a signal to themake-up valves 12 or 14 and a change in the feed will be made toreestablish the separating gravity to an acceptable level. For example,most of the magnetite fed to the cyclone will be of recirculatedmagnetite. Of the 25 TPH needed, approximately 24 TPH will enter thesystem through means 28. As a consequence, additional make-up magnetiteand/or water must be added. However, the relative proportions of theadditions may be changed to bring the separating gravity into line withthe desired values.

Thus, by monitoring the percent magnetite in the overflow, for example,it is possible to automatically adjust the input feed to the cyclone torestore the separating gravity of the cyclone to the desired level toinsure optimum separating conditions between the coal and refuse.

I claim:
 1. In a continuous method of beneficiating coal from refuse type material having a different specific gravity than coal by the steps of subjecting said coal and refuse to the operation of a dense-media cyclone, in which the dense-media thereof is a slurry of magnetite and water, and the separating gravity of said dense-media is controlled within predetermined limits, including (1) withdrawing beneficiated coal and media from said cyclone in the form of an overflow, (2) withdrawing refuse and media from said cyclone in the form of an underflow, and (3) replenishing the dense-media slurry lost in the overflow and underflow by adding separate flows of magnetite and/or water to the cyclone, characterized by the improvement of controlling said separating gravity by the steps of(a) selecting a desired separating gravity under which the cyclone is to be operated; (b) measuring the flow rate and percent magnetite in at least the stream of said overflow; (c) changing the relative proportions of the feed flow of magnetite and/or water to said cyclone when the percent of measured magnetite corresponding to an actual separating gravity is different from that of a desired percent magnetite corresponding to said desired separating gravity as shown by the relationship of FIG. 2 to return the actual separating gravity to said desired separating gravity; (d) continuously feeding untreated coal and refuse for treatment hereby to said cyclone.
 2. The method according to claim 1 wherein a portion of the magnetite from the overflow and underflow is recovered and recycled into said cyclone. 